Immunohistochemistry of CXCR2 in the synovium using immunoperoxidase and diaminobenzidine (brown) staining. (a) Section of rheumatoid synovium treated with a CXCR2 antibody. CXCR2 is expressed on macrophages in the intima. (b) Adjacent section to (a) treated with an anti-CD68 antibody. (c) CXCR2 is present in neutrophils in the rheumatoid synovium. (d) There was a lack of staining when sections were incubated with rabbit IgG instead of CXCR1 or CXCR2. Magnification × 380 (a), (b) and (d); magnification × 470 (c).